The invention relates to an electric hotplate with a hotplate body having connecting means for connection to apparatus lines. These connecting means in particular have connection portions leading away from the underside of the hotplate body and which belong to the heating resistor leads, whose position is substantially fixed with respect to the hotplate body. The connecting portions are advantageously formed by wire portion-like pins, which are admittedly inherently rigid under the forces occurring, but are also resiliently movable within certain limits.
Such electric hotplates are generally fixed in a hob in such a way that they engage in the assembly or mounting opening of said hob, are supported against the bearing forces with respect to the rim of said mounting opening and are connected at the underside of the hob to the apparatus lines belonging thereto. Although this connection offers very high reliability and safety if at least partly constructed as a plug or welded connection in such a way that with the apparatus lines is associated a connecting piece with an insulator, which is only connected to the electric hotplate or the connection portions on fitting the electric hotplate into the hob, but such a connection is not satisfactory for all the available assembly or fitting processes. Particularly if there can or is to be no welded connection or if the electric hotplate is inserted in the hob with an insulator already arranged thereon, or a construction of apparatus lines is to be used in which the connecting members of said lines have no insulator, the said known constructions are unsuitable.
An object of the invention is to provide an electric hotplate of the aforementioned type, which ensures a very simple assembly and an uncomplicated electrical connection, particularly if the apparatus lines are provided with the simplest possible connecting members at their ends.
According to the invention this object is achieved in the case of an electric hotplate of the aforementioned type in that the particular or each connecting pin has an in particular separate plugging piece which, in one or two directions at right angles to one another, is advantageously enlarged several times in cross-section compared with the wire cross-sections of the pin and forms a preassembled unit with the hotplate body. Thus, the apparatus lines, having at their ends as connecting members e.g. matching plugs or only multicore cable ends and which require no preassembled insulator connected thereto, can be connected to the plugging portions by a plugging process and as a result of their size and preassembled arrangement ensure a very safe and reliable electrical connection.
The plugging portion could admittedly be electrically conductively or mechanically rigidly connected to the connecting pin by crimping, appropriate one-piece shaping of the pin, a further plug connection or the like, but as a rule preference is given to a connection by spot welding, because this can be performed very easily during the manufacture of the electric hotplate, i.e. prior to its fitting in the hob.
It is also conceivable to construct the plugging piece as a negative plug with a plugging opening, as a substantially axially symmetrical or at least approximately circular or cylindrical plug pin or the like, but a very simple construction is obtained if the plugging piece is constructed as a flat plugging tongue, whose thickness need only be approximately the same as the diameter of the connecting portions and which as a commercially available standardized part is suitable for connection to matching plugs, which can be very easily fitted to the apparatus lines, e.g. by crimping. In order to bring about a space-saving housing of the adjacent plugging pieces of an electric hotplate, the largest cross-sectional extension of said plugging pieces is appropriately roughly at right angles to the plane of the cooking surface of the hotplate body and all the plugging pieces appropriately project forwards to the same extent and are arranged symmetrically to a common median plane parallel to the cooking surface.
A particularly advantageous further development of the invention provides for an insulator being provided for at least one plugging piece and in particular for all the plugging pieces together and said insulator can preferably be mounted from the free end of the plugging piece or pieces and therefore can be assembled following the fitting of the plugging pieces to the connecting portions, so that it is in no way prejudicial to said fitting operation. This insulator, which need only be mounted during the assembly of the electric hotplate in the hob, also appropriately forms a preassembled component of the hotplate body, i.e. prior to the installation of the plate in the hob, the insulator is at least partly placed on the particular plugging piece or the connecting portions and is fixed in this position in an appropriate manner so as to prevent automatic or accidental loosening.
Particularly if the plugging pieces or insulator in a view of the cooking surface of the hotplate body project at least partly over the circumference of a radially outer, downwardly projecting, circular flange rim of the hotplate body or even over the outer circumference of the complete hotplate body, difficulties can occur during the tight stacking of a plurality of such hotplates in a transportation stack. An advantageous hotplate stacking means can e.g. be gathered from German patent application P 37 28 541.6, to which reference should be made for further details. According to the invention, for such a stacking means it is in the present case provided that the stacking portion or portions or the plugging portion or portions or the insulator or insulators can be transferred from a stacking position into an assembly or connection position by means of resilient or bending deformation of the lead or leads, by pivotable or displaceable mounting supports of at least one of said parts or by similar measures and in which they are located further below the underside of the hotplate body and/or have a modified radial spacing from the circumference of the hotplate body or its central axis. In the stacking position, the corresponding parts are located appropriately between the planes of the top surface, i.e. the cooking surface, and the underside, i.e. roughly the plane of the lower circular face of the outer flange rim, so that the electric hotplate in the stacking state has no parts projecting outwards over said planes and consequently a minimum stacking height is obtained. Any necessary, hinge-like limited bending zones for transfer between the stacking position and the connecting position can be formed by weakened cross-sectional areas, by bent zones or the like of the leads, which are appropriately located as far as possible from the plugging piece, namely e.g. in the vicinity of the fixing of the connecting portions with respect to the hotplate body. This fixing is mostly brought about by an insulator fixed in the underside of the hotplate body, e.g. by fixing to a lower cover plate, which traverses the leads and on whose underside they are bent against the outer circumference of the hotplate body.
It is particularly advantageous for the finally assembled, i.e. the specified position of the insulator, if said assembly position is fixed by at least one securing member, whereby said securing can take place with respect to the hotplate body, the connecting pin and/or preferably the plugging piece. If the securing member is constructed as a self-locking snapping member or the like, then the retaining engagement is automatically obtained during the transfer of the insulator into its assembly position.
For a securing engagement of the insulator in the hotplate body, in its final assembly position the insulator appropriately engages on the face or the outer circumference or on both the said surfaces of the outer flange rim of the hotplate body, a small spacing with respect to said surfaces also being conceivable. As a result of this engagement on the one hand and the retaining element on the other, the insulator is locked in both movement directions roughly parallel to the connecting pins, so that it substantially forms a positionally rigid support of the plugging pieces with respect to the hotplate body, which only has to be engaged during the installation of the electric hotplate and which previously does not in any way impede the mobility of the plugging pieces, particularly at right angles to the plane of the cooking surface. Following the introduction of the insulator into its final position an orientation aid is provided, through which the plugging pieces are secured oriented in a precisely defined position and can also be connected using robots. Such a fully automated production is also possible in connection with the remaining assembly of the inventive electric hotplate.
The connecting portion of the hotplate appropriately extends at the most up to the outer circumference of the hotplate body or at the most to the inner circumference of the outer flange rim and preference is given to constructions according to DE-OS 35 40 816, to which reference can be made for further details. Thus, an electric hotplate constructed in said known manner can either be used for the connection possibilities described therein or, for the presently described connection possibilities only requires the fitting of plugging pieces or insulators. As in the present case the pins are relatively short, it is appropriate to provide a wire or flat bar-like connecting portion between the plugging piece located outside the outer circumference of the outer flange rim or the hotplate body and its flat extension is appropriately parallel to the cooking surface of the hotplate body, so that it forms a relatively easily bendable hinge portion at right angles to the cooking surface. This connecting portion can be constructed in simple manner in one piece with the plugging portion, e.g. as a stamped bent part.
However, it is also conceivable for the particular connecting pin to extend a relatively long way beyond the outer circumference of the outer flange rim or the hotplate body or for it to be constructed according to DE-OS 35 40 815, to which reference should be made for details. In this case, the pin can laterally overlap the plugging portion over part of its length or to such an extent that it approximately extends up to the plugging portion of the plugging piece to be engaged for producing the plug connection.
It is appropriate if the plugging piece has an in particular flat fixing portion with which the connecting pin is engaged. The weld can be provided on a flat or lateral face of the plugging piece, so that the latter projects laterally only roughly by its thickness over the connecting pin. In order to ensure a precisely defined and therefore particularly reliably performed welded joint, the plugging piece is provided for the purposes of receiving the weld with a stamped out arm or some similar stud or fin-like protuberance. The end of the connecting portion or pin can be flattened by crimping or the like, so that it has a smaller cross-sectional extension in one direction and a larger cross-sectional extension at right angles thereto than the remaining lead and consequently ensures a reliable connection with the plugging piece.
Instead of or in addition to the described constructions, it is also advantageously possible to provide on the plugging piece at least one clamping screw, which advantageously engages in a plugging hole of the plugging piece, in which the connecting pin and/or connecting member are inserted in overlapping manner and can be fixed with the clamping screw. This permits the advantageous electrical connection of at least one or all the connecting pins of the electric hotplate. Instead of or in addition to the described constructions, it is also possible to connect at least one or all the pins of the hotplate directly to the connecting member of the apparatus line, e.g. by a welded joint. Without using further parts, the connecting member is directly formed by the associated apparatus line end or preferably by a multicore cable end, which is fixed by crimping or the like to said line end and holds together the individual wire strands of the flexible apparatus line in the form of a holder. Possiblities of such a construction can be gathered from German patent application P 37 28 528.9, to which reference should be made for details.
For the connection of electric hotplates, it is also possible to use at least one socket as an electrical plugging connection, the electric hotplates generally being connected in two, three or four-pole manner. Such sockets appropriately have an electrically conductive socket body, which provides a cable connection for the electrically conductive and mechanically secured connection to the electric lead cable forming a plugging part optionally linearly connected thereto for mounting on a plug. In order to secure the socket against withdrawal counter to its mounting direction, in addition to its non-positive or frictional connection to the plug and with respect to at least one of the components engaged therewith, advantageously on the socket body is provided a rearwardly directed or acting withdrawal stop, which can secure the socket, e.g. against withdrawal from an insulator surrounding it or some other of the said components.
Thermally or similarly loaded, electrical plugging connections, particularly those provided on electric hotplates and which are continuously exposed to severe temperature fluctuations, over a period of time can become so loose as a result of scaling, corrosion and the like, that the electric line connection is interrupted. However, such plugging connections are desirable as a result of the simplicity of fitting and due to the easy replaceability of the unit to be electrically connected.
In order in particular to provide a socket of the aforementioned type which, in the case of simple construction and easy fitting, ensures a further improved and particularly durable position fixing in the plugged state, it is inventively provided that the socket body has an advance stop, which rigidly limits the plugging movement of the socket in its plugging direction with respect to a further component, particularly one which is separate from the plug, so that the socket can assume a precisely defined end position with respect to its movement direction, or conversely the further component, particularly the insulator, can be mounted on the socket in such a way that it assumes a precisely defined end position with respect thereto. The advance stop is advantageously located behind the front end of the plugging part or behind the centre of its length, or even behind the complete plugging part, so that it is positioned outside the zone where particularly high temperatures or thermal and/or electrical stresses can occur. Preferably, in addition to the advance stop, there is at least one withdrawal stop acting in the opposite direction, so that the socket can be positionally secured in both opposite directions in an almost clearance-free and non-positive manner with respect to the further component or components.
The insulator is mostly used for orienting or alinging the leads of the electric hotplate provided with the plugs with respect to the hotplate body, e.g. in that the insulator engages with alignment surfaces in the vicinity of the underside on the hotplate body or on its outer flange rim. In the case of said positional fixing of the socket with respect to the insulator by stops, the socket is kept in precisely oriented manner relative to the hotplate body, or conversely the insulator is not only secured against movements towards the central axis of the hotplate body in that it engages with corresponding shoulder faces on the outer circumference of the hotplate body, but it is also non-positively secured against movements in the opposite direction in that it is arrested by the advance stop of the socket.
The advance stop can have a limited, relatively rigid elasticity, so that it gives way slightly due to the counterpressure of the counterstop, e.g. up to the time when the withdrawal stop has reached the stop position, the advance stop moving back following relief, so that the further component having the counterstops is then pretensioned and is held in clearance-free manner between the stops. However, the advance stop can also be constructed in a substantially positionally rigid manner with respect to the socket and in this case there can also be a small longitudinal clearance of the socket between the two stop positions for corresponding uses. The socket is also suitable for other electrical plug connections than that of electric hotplates.
It is admittedly conceivable to form at least one advance and/or withdrawal stop by a separate part fixed to the socket or socket body, but the particular stop is preferably constructed in one piece with the socket body. Appropriately all the stops, particularly all the advance stops, are shaped in one piece onto the socket body. The particular stop can e.g. be formed by a simple leg or web-like bend of the socket body and in each case the particular stop appropriately projects outwards over the outside of the outer boundary planes of the plugging part or is completely located outside the plugging opening. In addition, the advance stop can also be formed by a forwardly directed surface or edge at right angles to the plugging direction and which is in any case already provided on the socket body. This is in particular constituted by the leading edges of a clamp-like, rear shank end of the socket body used for embracing the associated end of the insulating casing of the cable connected to the socket to form a unit.
In order to obtain an even more precisely defined stop position, either only a single advance stop is provided, or at the most two advance stops are provided, which are preferably located in the same stop plane and not, as is also conceivable, reciprocally displaced in the longitudinal direction of the socket. The same advantageously also applies with regards to the withdrawal stop.
The counterstop for the withdrawal stop or stops could also be located within the further component, particularly the insulator, but the reaching of the stop position can be controlled particularly advantageously if said counterstop is formed by the rear end face of the insulator or the like. The counterstop for the withdrawal stop is appropriately located behind the centre of the length of the insulator within the same. It can have a spacing from the counterstop for the advance stop or from the rear end face of the insulator, which is at the most as large as the material thickness which must be provided for maintaining an adequate insulator strength between the counterstops.
If the advance stop and the withdrawal stop are located on remote sides, particularly flat sides of the socket, in particular the withdrawal stop can be engaged in simple manner in its stop position by small tilting movements of the socket in the manner of a locking or snapping member. However, if said stops face one another on the same side of the socket, the engagement by transverse movements can in particular be facilitated if the e.g. single advance stop is laterally displaced with respect to the withdrawal stop or with respect to the median longitudinal plane of the socket. However, in any case, the stop or stops are located laterally within the lateral edges of the plugging part and/or laterally outside the cable connection shaft.
The socket body is appropriately constructed as a sheet metal shaped stamped bending part, so that the plugging part forms on one side a longitudinal gap, which is bounded by facing longitudinal edges of two sleeve or bending strips or flaps. The latter, e.g. by beading the longitudinal edge regions, can form elongated contact springs, which engage or slide with a relatively high spring tension on the plug. However, such beads generally only have a linear contact engagement, which can lead to high surface pressures and to undesired difficult fitting, which is particularly advantageous if several sockets combined into a unit are to be simultaneously mounted on a corresponding number of plugs, because then the difficult fitting can then be increased by the factor of said number. Despite the good contact resilience, this can be avoided in that the contact springs are constructed in leaf or strip-like manner and consequently form a correspondingly wide sliding or engagement surface for the flat plugs. The total width of said sliding or engagement surface on one side of the plugging part can e.g. be approximately half the width of said flat side. It is also advantageous if the contact springs are set back with respect to the front and/or rear end of the plugging part, or are shorter than the latter. The effective engagement or bearing surface for the plug can have a length which is smaller than half the length of the plugging part.
A further important advantage can be obtained in that the particular contact spring forms at the front end an insertion bevel for the flat plug, which can e.g. be achieved in that the front end connects in one piece to the casing of the plugging part, whereas both the lateral edges of the contact spring are free or exposed and one lateral edge can be directly formed by the longitudinal edge of the associated sleeve flap. Each of the two juxtaposed contact springs, whose rear ends can also pass in upwardly sloping, one-part manner into the casing or sleeve flap of the plugging part, extends over more than half the width of the associated sleeve flap.
A particularly advantageous further development of the invention is constituted by the fact that facing contact springs engaging on opposite sides of the plug are provided. Appropriately, in each case two contact springs face one another pairwise and can have approximately the same width. However, the facing contact springs appropriately have varyingly long sliding or engagement faces. One contact spring by in side view flat curved construction forms an approximately only linear sliding or engagement face over its width, as well as the portions rising at an acute angle, whilst the other contact spring has a longer, approximately linear top or vertical portion, which passes into obtuse-angled end portions. The contact springs forming curved or linear sliding and engagement faces are appropriately located in the vicinity of the sleeve flaps, whilst the contact springs with the elongated top portion are advantageously directly connected on either side by means of waste-free stamped edges to the lateral edges of the withdrawal stop. The free, rearwardly directed end of said withdrawal stop appropriately projects in acute angled manner over the associated outside of the plugging part and its front and rear end can substantially coincide with the associated ends of the adjacent contact springs, so that the length ratios given for the same can also apply with respect to the withdrawal stop.
As a result of the described construction, the plugging part is formed by a front and a rear, in each case clamp or clip-like casing part, which are interconnected by means of several longitudinal webs distributed in spaced manner over the circumference or whose connecting part has several circumferentially distributed longitudinal slots, whereby lateral, planar longitudinal webs located on the narrow sides of the plugging part can be narrower than the latter and can be slightly wider than the plug thickness. The longitudinal webs on the flat sides are exclusively formed by the contact springs.
For the locking longitudinal securing of the socket with respect to the plug, the socket can have a spring cam projecting into its plugging opening between its ends and which engages in a corresponding depression or opening of the plug. According to the invention, said spring cam is provided in the vicinity of the sleeve flaps and not on the side facing the latter, but as a result of corresponding shaping of the longitudinal edges of said sleeve flaps, it is still in the median longitudinal plane of the plugging part. In order that the longitudinal slot between the sleeve flaps does not for this purpose have to be laterally displaced with respect to the median longitudinal plane over the entire length thereof, it is only displaced in the vicinity of the spring cam, whereas the forwardly and/or rearwardly connecting longitudinal portions of the longitudinal slot are located in said median longitudinal plane. This also leads to a flap-like projection, which projects laterally and carries or forms the spring cam and which ensures particularly good spring characteristics. It is advantageous in this case if the spring cam is located in the vicinity of or on a contact spring and is slightly forwardly displaced with respect to its apex or with respect to the centre of its length, so that it is inclined in cross-section under a few radians in the direction of the plugging end of the socket and is directly connected to the insertion bevel.